1. Field of the Invention
The present invention relates to a facsimile apparatus, printer, copier or similar image forming apparatus and more particularly to an image forming apparatus of the type transferring a toner image from an image carrier to a movable belt side at a nip between the image carrier and the belt.
2. Description of the Background Art
It is a common practice with an image forming apparatus to hold a photoconductive drum or similar image carrier and a movable belt in contact for thereby forming a nip for image transfer therebetween. In this condition, a toner image is transferred from the image carrier to the belt side. The belt is implemented as, e.g., an intermediate image transfer belt or a sheet conveying belt. The intermediate image transfer belt allows a toner image to be transferred from the image carrier thereto at the nip, conveys the toner image to a secondary image transfer position, and then transfers the toner image to a sheet or recording medium. The sheet conveying belt simply conveys a sheet to which a toner image is to be directly transferred from the image carrier. In any case, a toner image is transferred from the image carrier to the belt side at the nip.
The problem with the image forming apparatus of the type described is that a portion of the belt upstream of the nip is apt to slacken due to short tension or a reaction to occur at the beginning of drive. Such a slack of the belt disappears little by little as the time elapses after the start of drive of the belt. However, the speed at which the surface of the belt moves, as measured at the nip, delicately varies before the slack fully disappears. If a toner image is transferred from the image carrier to the belt or a sheet being conveyed thereby when the belt speed is varying, then the toner image is distorted, dislocated or otherwise disfigured. In light of this, it has been customary to start the transfer of the toner image on the elapse of a preselected period of time since the start of drive of the belt. This extra period of time extends the image forming time.
Technologies relating to the present invention are disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 11-65204, 2000-250281 and 2001-228672.